Recent laws, codes, ordinances and the like have levied requirements mandating public buildings to be made more accessible to those with disabilities. One such law, the Americans with Disabilities Act, enacted in the United States, has had a profound impact on building codes throughout the United States. As a result, many buildings, in addition to hospitals, now provide an automated means for entry, also known as an automatic opening system, for use by handicapped persons.
A basic automatic opening system generally comprises an activating device and an operating device. A handicap access door with this system typically functions by pressing on a large square activation device which is colored blue. This activation device then communicates with an operating device which causes the door to open. For example, a system can incorporate a shaft connected to a piston within a cylinder. Upon activation, a hydraulic fluid is pumped into the cylinder forcing the piston and shaft to move. Thus the door is moved from an initially closed position to an open position. The door is maintained in an open position for a predetermined period of time after which the door is returned to its normally shut position. In the case of an hydraulic system incorporating a spring, the operating device may de-energize the pump and open a vent in the cylinder. The spring then operates against the piston through the shaft and the door, to push the fluid out of the cylinder while closing the door. Alternatively, a system can be designed to use hydraulics in place of a spring by pumping fluid to the opposite side of the piston, and forcing the door shut.
When constructing buildings, it is possible to hard-wire the activation device to the operating device. However, for buildings which were constructed without a handicap access door, hard-wiring the system is frequently impractical. To overcome this problem, automatic garage door activating systems have been adapted for use in handicap access applications. A basic automatic opening system is installed by placing two transmitters on opposite sides of a door. Since the transmitter is battery operated, there is no need to constrain the location of the transmitters due to power availability. Typically, the transmitter is located behind a blue plate at a point near the door.
The receiver is located near the operating mechanism for the door. In many applications, the power source used to operate the door is not compatible with the power source requirements for the receiver. Consequently, transformers and or rectifiers are used to supply the proper source of power. The receiver is then wired to control the desired door operating mechanism and other accessories such as magnetic locks. However, since the receiver is not protected from inductive surges that result when activating devices such as magnetic locks, a separate source of operating power is needed.
However, garage door activating systems designed for objectives or features result in systems which are at odds with the design objectives or features of many automatic door opening systems used to permit access by disabled persons. For example, at one time, it was not unknown for one garage door activating system transmitter to operate with more than one garage door in a neighborhood. This was a very unsafe condition and new systems were designed with tighter parameters so as to reject all signals other than the signal of a transmitter specifically associated with the garage door activating system.
One design feature to address this issue was to reduce the margin for error in the system and reject “marginal” signals from a transmitter, i.e. signals which are slightly off the frequency a receiver is tuned to, or which have some noise or static in the signal. The signal may also be marginal if the transmitter has a clock running at a speed different than the clock of the garage door activation system receiver. In this situation, the transmitter and receiver can lose synchronization. This results in the receiver misidentifying even a valid incoming code and rejecting the signal as invalid. Thus, the receiver is designed to only accept signals with little or no static and which are within a narrow frequency band. Further, the transmitter must have an internal clock running closely to the speed of the receiver's clock or the transmission will not maintain synchronization, and the signal will be rejected. When applied to automatic door opening systems, this leads to a high and unacceptable failure rate. In other words, the door does not open when a person activates the system, constituting a failure. The problem can be further exacerbated by the use of parts with low quality standards which results in frequency drift and high error rates over the life of the transmitter.
Additional failures result from the use of transmitters with degraded batteries or degraded performance due to temperature variations. Both of these conditions can lower the voltage supplied to the transmitter and can affect both the frequency of transmission and the internal clock of the transmitter. One invention which addresses this performance issue is U.S. Pat. No. 5,831,548, Fitzgibbon. Fitzgibbon discloses the use of an inductor coupled to a storage capacitor which functions to maintain a constant voltage supply to the transmitter's oscillator even when battery voltage is starting to degrade. In essence, the battery charges the capacitor while the transmitter is not in use. Upon activation of the transmitter, the capacitor “boosts” the battery and maintains the proper voltage for a short period of time. However, as the battery continues to degrade or the transmitter gets cold, it will take a longer period of time to recharge the capacitor, and eventually, the voltage will not be maintained at the correct voltage during activation of the transmitter.
In addition to applications for general public use, garage door activating systems are used in automatic door opening systems in compound type settings such as a college campus. In a compound setting, several buildings will have automatic door opening systems. However, rather than allowing the general public access to the buildings, only certain individuals are desired to have access to the buildings through these automatic doors. Thus, authorized users are given individual transmitters to be used with the particular RF door opening systems within the compound.
The compound setting presents certain unique problems. As new entrances are provided, they must be fitted with receivers compatible with the existing transmitters. However, commercial garage door operating systems use different frequencies, requiring specific activating devices which transmit at a frequency unique to the receiver. Consequently, upgrading a system can require wholesale exchange of transmitters. Alternatively, U.S. Pat. No. 5,841,390, Tsui, discloses a receiver which is capable of operating with a plurality of transmitters at different frequencies, each transmitter having its own unique code. However, once the Tsui receiver learns the proper codes and frequencies, the receiver operates similarly to other receivers. Thus, for safety purposes, the receiver will reject marginal signals. Therefore, Tsui does not solve the problem of failures resulting from degraded transmitter performance due to battery degradation or environmental conditions.
U.S. Pat. No. 5,793,300, Suman et al., discloses a system which includes an RF receiver which performs a frequency scan when in training mode in order to identify signals at different frequencies. Thus, Suman et al. is useful when a new transmitter is to be used with a system. However, since the frequency scan occurs only in training mode, it is not useful for adjusting to a signal which is changing due to voltage differences during a given transmission or between uses.
Another limitation for garage door openers in the compound setting is that as transmitters fail or are lost, they must be replaced with transmitters which are compatible with the existing receivers. This becomes increasingly difficult as a system ages and replacements are harder to find. Further, incremental improvement of the system, so as to spread improvement costs over a number of years, is impacted. U.S. Pat. No. 5,854,593, Dykema, addresses this problem. Dykema discloses a transmitter/receiver which learns the characteristics of received RF signals and can store and transmit the learned signals. The Dykema transmitter learns the particular signal characteristics when placed into training mode. The learned signal is then stored for use when a particular button on the transmitter is pushed. While this approach is very useful in many scenarios, it has certain intrinsic limitations. Included among these is the fact that the transmitter must be trained for each new receiver. Additionally, the problem of deteriorating transmitter performance is not addressed. Another limitation is that the number of receivers a particular transmitter can be used with is limited to the number of transmit buttons built into the transmitter, unless one “trains” the transmitter each time a new receiver is encountered.
A limitation of garage door openers in many settings is that the receiver for garage door openers are not designed to provide operating power to inductive loads, i.e. devices incorporating coils. However, it is common practice in automatic doors to incorporate inductive load accessories such as magnetic locks, locks and electric strikes into the door operating system. The problem is that when current to a device having a coil is changed, the coil causes a voltage spike or surge. Therefore, if a system without surge protection is used to drive an inductive load, the voltage spike will burn out the system. However, it is preferable to provide operating current to the inductive loads through the activating system receiver to avoid the need for an additional power source and wiring. Consequently, systems relying on commercial garage door openers to drive inductive loads require the addition of surge protectors external the receiver. This results in extra space requirements as well as increased installation planning, equipment, and time.
A related limitation of retrofitting a building with garage door openers concerns the provision of an appropriate power source. The nearest available power source for a given installation location may vary between 12 and 40 volts. However, garage door opener receivers typically operate on 24 VAC power. Thus, if the proper power supply is not available, the installer of the door opening system must either accept the difficulties associated with providing a new power source, carry a variety of receivers for use with different voltage sources, or provide an appropriate assortment of voltage transformers. All of these options significantly increase the complexity of an installation, resulting in excessive planning, material, and labor costs.
The difficulties described above are further exacerbated when it is desired to automate doors in a timed sequence. This application is encountered with buildings having two sets of doors in sequence as is common in entry vestibules. One approach to automating such a building is to use a receiver capable of issuing two timed signals. U.S. Pat. No. 5,793,300, Suman et al., discloses a receiver with this capability. In Suman et al., a first signal is generated which can, for example, turn on a light. At a predetermined interval, a second signal is generated by the receiver to turn the light off. Since two signals are generated, it is conceivable that the first signal could be modified such that a first door is opened, and the second signal could be modified such that a second door is opened. Alternatively, U.S. Pat. No. 5,095,654, Eccleston discloses a receiver which can be used to instigate sequential operations such as manipulating a deadbolt mechanism and then opening a door, although the Eccleston, receiver generates only one signal. Eccleston uses the signal to initiate a sequence of events. However, the receivers of both Suman et al. and Eccleston suffer from the same defects. Namely, they require physical connections between the two doors to be operated, either electrical connections as in Suman, or operating system connections as in Eccleston. Consequently, the benefits of using an RF system are lost.
A particularly irritating shortcoming encountered when using garage door openers in a door activation system is that the transmitter only has operating power applied when its activation switch is depressed. Consequently, it is a common occurrence to depress the switch and let the switch return to its normal condition, only to discover that the door has not been operated. The failure of the system frequently traces to the fact that the switch was not depressed for a sufficiently long period of time. Consequently, an individual is forced to repeat activation of the transmitter. This is frequently accomplished by depressing the switch for an excessive period of time. This operating characteristic, common in garage door openers, is very undesirable in a door activation system.
What is therefore desired is an RF door activation system which is easy to retrofit into existing buildings. The system should not require the use of complicated or expensive transmitters. The system should be useful with a variety of transmitters having differing frequency and frequency drift characteristics without the need to initiate a training mode. It is desired that the system minimize the effect of timing errors. Further, the system should be capable of driving inductive loads without the need for bulky or expensive add-ons. It is further desired that the system be compatible with a variety of power sources without the need for external adapters. It is also desired to realize an inexpensive and dependable transmitter capable of signaling a plurality of receivers upon a single activation of the transmitter. The system should also be capable of transmitting for a preprogrammed period of time even if the activating switch is only activated momentarily.